1. Field of the Invention
The present invention relates to a method and apparatus for modifying a graphics display image. Such a graphics display image may be, for example, a map, circuit diagram or schematic plan, which is made up of a plurality of components.
2. Summary of the Prior Art
It is known to form a graphics display image on a display screen of a suitable display device, by reading or scanning a print (hard-copy) of the image that is to be displayed. The print may be a map, construction blueprint, circuit diagram, design drawing, etc, and may thus include lines, symbols, shadings, etc, which are read by a suitable reading apparatus, and converted to digital data. Once the data is accurately stored in a suitable memory, it can be displayed on a display screen and modified or processed electronically, as desired. Thus, for example, if the print is a map, data representing that map can be stored in a computer, presented on a display screen, and manipulated in order to show a desired part of the map, a desired section through the map etc.
In order to generate the data representing a graphics display image, the print must be read optically, and the resulting data stored. In practice, that data is vector data, i.e. data representing the X and Y coordinates of a multiplicity of points in the image, and the graphics display image is then reproduced from the vector data. However, when a print is read by suitable optical reading apparatus, there are likely to be errors in the reading of the vector data, e.g. due to the thickness of lines, etc on the print, and therefore the displayed graphics display image will not correspond exactly to the original map. Therefore, it is normally necessary for the data representing the graphics display image to be edited before it can be used reliably.
JP-A-63-108430 discloses a system in which an image is formed by characters and image components which are located in separate parts of a display, and in which at least the characters could be replaced. During this replacement (editing), the character part of the display could be emphasized by high-lighting it relative to the part of the display bearing the image components. It can readily be seen that such an arrangement is of limited application only, as it is not always possible to separate a graphics display image in the way proposed in JP-A-63-108430.
In JP-A-57-134738, a graphics display image is divided into a plurality of blocks, each block containing one or more image components, and a block to be edited is high-lighted. Then, the operator prepares a separate, correct, version of the block which is then used to replace the block to be edited in the graphics display image.
In JP-A-57-134738, the block to be edited is high-lighted. More generally, it is well known to high-light part of a display, or to reduce the intensity of parts of a display to emphasise other parts, and examples are shown in JP-A-58-3056, JP-A-61-269194, and U.S. Pat. No. 4,601,021. In JP-A-58-3056, parts of a display of a three-dimensional image are deleted from the display (i.e. their intensity reduced to zero), if they are not visible from the viewing point of the three-dimensional image. In JP-A-61-269194, individual components of a graphics display image may be read and combined together, and some of those components may be high-lighted, or the intensity of others may be reduced, for emphasis. In U.S. Pat. No. 4,601,021, selected components of a graphics display image may be modified by deletion (reducing intensity to zero) of the components not desired, or blinking or otherwise high-lighting the desired components. It should be noted that in JP-A-58-3056, JP-A-61-269194, and U.S. Pat. No. 4,601,021 the disclosure is concerned only with emphasizing parts of the graphics display image, not with editing.
It is also known, from JP-A-62-60067, to provide a visual distinction between graphics display image components which already exist in a database of such components, and newly added components. In JP-A-62-60067, the existing components are shown as thick lines, and the newly added components are shown as thin lines.